Meaning of “foil” - Learner’s Dictionary

foil

noun uk us /fɔɪl/

[ U ] metal made into very thin sheets like paper and used mainly for covering food:

UK aluminium foil/ US aluminum foil
a foil for sb/sth

a person or thing that shows or emphasizes how different someone or something else is

(Definition of “foil noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)